Corrosion-resistant razor blades

ABSTRACT

STEELS SUITABLE FOR MAKING CORROSION-RESISTANT RAZOR BLADES CONTAIN CHROMIUM AND CARBON, AND MAY CONTAIN SILICON, MANGANESE, MOLYBDENUM, TUNGSTEN, COPPER, COBALT, NICKEL, NIOBIUM, TANTALUM, TITANIUM, VANADIUM, ZIRCONIUM, BORON OR BERYLLIUM. THE RATIO OF CHROMIUM TO CARBON IS LESS THAN 30:1; THE CARBON CONTENT IS 0.3-0.5 WT. PERCENT; THE SILICON CONTENT IS WITHIN THE RANGE 0.8-2.0 WT. PERCENT, AND THE CHROMIUM CONTENT IS 9-.-10.8 WT. PERCENT. A TOOL FORMED FROM A STEEL OF THIS CLASS HAS A HARDNESS EXCEEDING VPN 800 IN THE HARDENED CONDITION, AND A HARDNESS AFTER TEMPERING UP TO 45-0*C. WITHIN THE RANGE VPN 720850.

June 27, 1972 3,672,877

JAN'CHRISTER H. O. CARI-EN ETAL CORROSION-RESISTANT RAZOR BLADES Original Filed Sept. 5, 1967 INVENTORS Vzm'mw fiwum United States Patent 015cc 3,672,877 Patented June 27, 1972 3,672,877 CORROSION-RESISTANT RAZOR BLADES Jan-Christer Henric Ovesson Carlen and Claes Bertil Bergqvist, Sandviken, Sweden, assignors to Sandviken Gernverks Aktiebolag, Sandviken, Sweden Continuation of application Ser. No. 665,320, Sept. 5, 1967. This application July 27, 1970, Ser. No. 64,087 Claims priority, application Sweden, Sept. 22, 1966, 12,737/ 66 Int. Cl. C22c 39/14, 39/48 US. Cl. 75-126 C 3 Claims ABSTRACT OF THE DISCLOSURE This application is a continuation of our parent patent application Ser. No. 665,320, filed Sept. 5, 1967, now abandoned.

The present invention relates to improvements in corrosion-resistant steel razor baldes. In addition to a good corrosion resistance they have a high cutting edge hardness and a structure free from deleterious carbide grains. The cutting edge hardness exceeds 800 Vickers (0.5 kg. load) (VPN 800) after the hardening of the steel, and 720 Vickers (VPN 720) when tempered up to 450 C. subsequent to the hardening. The invention also comprises a method of manufacturing such, blades.

It previously has been known to produce corrosionresistant edge tools such as razor blades from high-chromium steels having high or medium high contents of carbon and hardened from a temperature exceeding 1000 C. As examples there can be mentioned steels containing 13-14% chromium, 0.91.1% carbon (type A) and 13- 14% chromium and -07% carbon (type B), the remainder being substantially all iron with or without minor additions of one or more further alloying elements such as manganese, copper, molybdenum and cobalt. The tools or blades made from these steels have been found not entirely satisfactory in several essential respects. Thus, the steels of type A when hardened to a hardness close to 800 Vickers (VPN 800) assume a structure including a large number of coarse carbide grains within the range of 3-30 micron (maximum linear dimension) which render it impossible to obtain a smooth cutting edge on a tool of this steel, as these grains are easily torn out during the grinding of the cutting edge and give the edge a frayed contour and surface. Moreover, the corrosion resistance of these steels is only moderate. Steels of the type B have less coarse carbide grains and a somewhat better corrosion resistance than have the steels of the forementioned type, but the maximum hardness obtained by hardening is less than that for type A, which adversely influences the duration of edge sharpness of the blades manufactured from the same.

The purpose of the present invention is to provide corrosion-resistant blades such as razor blades having an improved corrosion resistance in combination with superior edge sharpness and smoothness and improved temper resistance.

The appended drawing is a schematic diagram showing the preferred contents of carbon and the sum of chromium, one-half of the molybdenum and one-quarter of the tungsten of a steel composition exemplary of the present invention. Said sum is designated Y in the diagram.

According to the invention the razor blades, are made from a steel having a very good corrosion resistance and a hardness exceeding 800 Vickers (load 0.5 kg.) (VPN 800) in the hardened condition and a hardness after tempering up to 450 C. exceeding 720 Vickers (VPN 720) and being within the range 720-850 Vickers (VPN 720- 850) depending on the tempering temperature. The steel, which has good workability, such as excellent cold rolling properties, is characterized in that it contains 0.300.50% carbon; 9-11.5% chromium; 0.8 2% silicon; 01.0% manganese; 0l.5% molybdenum; 03.0% tungsten and 0.1% each of a member of the group consisting of nickel, cobalt, copper, niobium, tantanium, vanadium, zirconium, boron and berryllium, the total of all the last said members being a maximum of 1%; and the remainder being substantially all iron, and in which the carbon and the sum of the chromium, one-half of the molybdenum and one-quarter of the tungsten are present in amounts which are defined Within the area ABCDEFA in the accompanying diagram, wherein the said sum is designated Y. Thus when a low carbon content is chosen we have found that the chromium contentand, molybdenum and/or tungsten are present, the sum of the chromium content, onehalf of the molybdenum content and one-quarter of the tungsten contentshould also be low. The limiting conditions defined by the co-ordinates of the area ABCDEFA are the following: A, /03; B, 11.25/03; C, 12.25/04; D, 12.25/05; E, 10.0/0.5; and F, 9.0/0.4.

Normally, the carbon content should not exceed 0.45%, e.g., be within the range 0.35-.45%. Further, the chromium content should as a rule be held within the range 9.25-11.0%, and preferably -11%. The sum of the contents of chromium, one half of the molybdenum and one-quater of the tungsten preferably should be held within the range 9.51l.75%. The preferred amount of carbon and the sum designated Y of the amount of the chromium, one-half of the amount of molybdenum and one-quarter of the amount of tungsten are defined within the area A B C D E F A in the accompanying diagram in which the co-ordinates are the following: A 9.5/0.35; B 11.25 0.35; C 11.75/0.40; D 11.75/0.45; E 10.0/0.45; F 9.5 0.40.

The content of molybdenum should normally be chosen within the range 0.3-1.5 Often it should exceed 0.5 and a preferred range is 0.71.3%. The content of tungsten preferably should be, at the most, 2.6%. The silicon content preferably should be 0.9%-1.5% and the manganese content 0.20.7%. The amounts of each element of the group consisting of nickel, cobalt, copper, niobium, tantalum, titanium, vanadium, zirconium, boron and beryllium normally should not exceed 0.5%, and the total of all these elements should also not exceed 0.5%.

The steels previously used for edge tools such as razor blades have had a non-balanced composition, which means that their contents of carbon and chromium have been in excess of what would be useful when the steel was hardened. Thus the surplus of carbon and chromium has been found as carbide grains in the hardened steel while the matrix has had substantially less carbon and chromium contents than could be learned by the chemical analysis of the steel.

According to the present invention the composition should be balanced in such a way that the analysis of the steel and that of the matrix are substantially the same. One of the advantages gained by the steel according to the invention is that the composition of the matrix after hardening will be practically constant irrespective of changes in the hardening conditions. This means that also the corrosion resistance will be unchanged and that the steel is insensible to changes in the heat treatment conditions. Due to the relatively low contents of carbon and chromium present in the steel of the present invention the steel is practically free from primary carbides, which circumstance is of great importance for the achievement of excellent cutting blades. In the hardening of the steel any carbides present are practically completely dissolved whereby the chemical analysis of the matrix will be the same as the analysis of the steel. The fact that the composition of the matrix decides the corrosion resistance of the hardened steel contributes to the excellent corrosion resistance of the steel according to the present invention. A further advantage in comparison with the previous corrosion-resistance steels is the lower content of chromium which is of importance with respect to costs.

The hardness of the steel depends on the carbon content of the steel. However, if the M,,-temperature of the steeli.e., the temperature when the transformation of austenite into martensite beginsis unduly lowered by the addition of too high amounts of alloying elements to the steel, the austenite transforms only partly into martensite with the result that the hardness will not be sufficiently high even if a martensite-promoting low-temperature cooling is practiced. The prior steels used for the manufacture of corosion-resistant edge tools such as razor blades have not had compositions conveniently balanced and hence the maximum hardness reached by these steels has been considerably less than wanted. Nor has it been possible by these steels to obtain such a uniform composition in the matrix as in the steel according to the present invention. Thus the presence of large amounts of carbide grains in said prior steels gave rise to variations in the chemical composition around the grains, which in turn reduced the maximum hardness obtainable by hardening.

The superior properties of the steel according to the invention in comparison with previously used corrosionresistant steels for razor blades will be further explained in the following by way of examples.

The structure of the steel as cold-rolled is of considerable importance for producing an excellent edge. Thus the presence of coarse carbide grains is a serious disadvantage, as they (as was earlier mentioned) are easily torn out during the grinding of the cutting edge and give the edge a frayed contour and surface.

In the example below the steels A and B represent previously used razor blade steels while the steels C1 and C2 represent steels according to the invention.

Carbide grains per mm.

Percent; coarser than 5 O Si Mn Cr Mo microns The hardness of corrosion-resistant chromium steels depends on the temperature used for the hardening, the cooling from the hardening temperature and the tempering temperature. For steels which contrary to the steel according to the invention-do not have a balanced composition, there is always by a fixed hardening time and a fixed cooling method only one hardening temperature, which gives maximum hardness. By subsequent tempering at 100-150" C. it is possible somewhat to increase said hardness. In the following examples in which steels A and B represent prior razor blade steels and C1 and C2 razor blade steels according to the invention the maximum hardness was obtained by using a hardening time of 40 seconds, a cooling from the hardening temperature to room temperature and thereafter to 70 C. and a subsequent tempering at 100 C. in boiling water.

Maximum hardness Percent Vickers (load 0.5 kg.)

0 Si Mn Cr (V PN) The higher hardness of the steels according to the invention facilitates edge grinding, improves the edge quality and contributes also to a prolongation of the useful life of the edges ifas is common-the edges are coated with a fluorocarbon or other material for enhancing the shaving characteristics, in which event the blades as a rule are tempered at a temperature within the range 200-400 C. The final edge hardness depends on the temper resistance of the steel when tempered within said range. A comparison of the temper resistance of the prior steels A and B and the steels C1 and C2 according to the invention when tempered at 350 C. is made in the table below:

Maxim um Percent hardness Vickers C Si Mn Or Mo (load 0.5 kg.) 1

1 After tempering at 350 C. (V PN).

hardness.

Corrosion rate, mm./year A 98 B 5.0 C1 5.2 C2 4.8

It appears from the table that the corrosion resistance of the steels C1 and C2 was considerably higher than that for the steel A and equivalent to that for the steel B in spite of the lower content of alloying elements in the steels C1 and C2.

The invenion also relates to a method for the manufacturing of razor blades from steels according to the invention. The steel is cold rolled in strip form to the desired thin dimension, e.g., 0.05-0.5 mm., after which a shaping, e.g., punching, may be done. The cold-rolled steel strip is then hardened to high hardness by heating to a temperature within the range 1050-1125 C., preferably about 1100 C., with subsequent cooling to room temperature or lower, e.g., in the range between -20 C. and 120 C. After the hardening and a possible subsequent tempering within the range 75-125 (3., preferably about C., to a hardness level exceeding 800 Vickers (V PN 800), the cutting edges are shaped by grinding or the like. Finally, the material may be tempered during a limited period of time, for instance, for about a minute up to one or a few hours, at a temperature up to 450 C., e.g., within the range ZOO-400 C. The hardness of the steel after said final tempering is at least 700 Vickers (VPN 700) and lies within the range 720-850 Vickers (VPN 720-850) when tempered between 200-400 C., depending on the temper temperature.

All the percentages mentioned throughout this specification and in the appended claims are percentages by weight. The invention is of course not limited to the described embodiments but comprises any product within the scope of the appended claims.

We claim: 7

L Corrosion resistant razor blades having improved corrosion resistance in combination with superior edge hardness and smoothness and improved temper resistance, said razor blades having a cutting edge hardness above 800 Vickers (load 0.5 kg.) (VPN 800) when hardened by heating to 10501125 C. and thereafter cooling to a temperature at least as low as normal room temperature and above 720 Vickers (VPN 720) when tempered up to 450 C. subsequent to hardening, the razor blades being made from a steel consisting of in part by weight, 0.35-0.45% carbon; 9.25-11% chromium; 0.8- 2% silicon; 0-1% manganese; v0.5-4.5% molybdenum; 0-3% tungsten and 0-1% each of a member of the group consisting of nickel, cobalt, copper, niobium, tantalum, titanium, vanadium, zirconium, boron and beryllium, the total of said members being a maximum of 1%; and the remainder substantially all iron; the carbon content, and the sum of the chromium content, one-half of the molybdenum content, and one quarter of the tungsten content of said steel falling within the area A-BCDEFA in the accompanying figure.

2. Razor blades as claimed in claim 1, in which the silicon content is 0.9-1.5%.

3. Razor blades as claimed in claim 1, in which the molybdenum content is 0.71.3%.

References Cited OTHER REFERENCES Metals Handbook, 8th Ed., American Society for Metals,

vol. 1; p. 409 and 432, 1961.

L. DEWAYENE RU'I'LEDGE, Primary Examiner I. E. LEGRU, Assistant Examiner US. Cl. X.R.

-34654; -125, 126 F, 126 G, 126 P, 128 R; 14837 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 7 g77 D t June 21. 1972 lnventofls) Jan Christer Henric Ovesson Carlen and @laes Bertil Ber vist It 13 certified that error appe s in the above-identified patent and that said Letters Patent are hereby corrected. as shown below:

Please change the name of the Company in the heading of the patent:

Note that the name of the Company as printed:

"SANDVIKEN GERNVERKS" should read e; SANDV'IKENS JERNVERKS Signed and sealed this 22nd day of May i973.

(SEAL) Attest; I

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PC4050 nosg) USCOMM-DC 60376-P69 t U.S. GOVERNMENT PRINTING OFFICE I969 O366--33lr 

